The present invention relates in general to microfabricated devices for grasping, manipulating, and excising microstructures, such as microcomponents or biological structures, and more specifically to microtools having grasping and manipulating mechanisms, such as arms, and mechanical actuator(s) for precisely manipulating the mechanisms for grasping, releasing, rotating, or cutting an object or biological component.
Extraordinary advances are being made in micromechanical device and microelectronic device technologies. Further, advances are being made in MicroElectroMechanical Systems (“MEMS”) which comprise integrated micromechanical and microelectronic devices. The term “microcomponent” is generically used herein to encompass microelectronic components, micromechanical components, as well as MEMS components. A need often arises for a suitable mechanism to grasp microcomponents. For example, a need often arises for some type of “gripper” device that is capable of grasping a microcomponent in order to perform pick and place operations with the microcomponent. Pick and place operations may be performed, for example, in assembling/arranging individual microcomponents into larger systems.
With the advances being made in microcomponents, various attempts at developing a suitable gripper mechanism for performing pick-and-place operations have been proposed. This is discussed in the Handbook of Industrial Robotics, by Shimon Y. Nof, chapter 5, for example. Gripper mechanisms that comprise arms that are translatable for grasping a microcomponent using an external, macro-scale translating mechanism have been proposed in the existing art. For example, U.S. Pat. No. 5,538,305 issued to Conway et al. discloses a gripper mechanism that comprises a relatively large mechanism (including a servomotor, drive mechanism, screws, etc.) for controlling the movement of two arms that are coupled thereto. In the Conway et al. patent, each of the arms themselves include a forceps portion that is approximately 7.5 inches (or about 19.05 centimeters) long, which extends from the mechanism that controls movement of the arms. Attached to and extending from the forceps portion of each arm is a replaceable tip that is approximately 1 inch (or about 2.54 centimeters) long. Accordingly, in addition to the relatively large size of the mechanism for controlling movement of the arms, the arms themselves extend from the mechanism a length of over 20 centimeters. Thus, while such gripper device may be utilized for grasping microcomponents, the gripper device is not a micro-scale device, but is instead a relatively large device.
Variations in macro-scale translating mechanisms are presented in U.S. Pat. No. 5,895,084 issued to Mauro. In this approach, precision engineering is required to fasten or screw individual arms of the gripper to a support block. The requirement of the fastener(s), lead screw(s), cam drive(s), and other macro-sized components places substantial limits on the operation of the device and makes this device unsuitable for microfabrication. The structure and size of the Mauro device limits the minimum size of the objects it can manipulate. Furthermore, this complication limits the resolution with which the tweezers can be rotated or three dimensionally positioned. The precision manufacturing techniques required to produce the microgripper are expensive, and this expense, coupled with the complex internal structure, reduces the modularity of the Mauro microgripper. Therefore, it is expensive and difficult to swap out or replace microtools of various shapes and sizes.
Additionally, microgripper devices (e.g., those fabricated using a microfabrication process) have been proposed in the existing art. As described more fully below, microgripper devices have been proposed that comprise grasping mechanisms (e.g., arms) and a microactuator mechanism (e.g., electrothermal actuator or electrostatic actuator) for moving the grasping mechanisms for grasping a microcomponent. Such microactuator mechanisms may be included within the grasping mechanism. For instance, the arms of a microgripper device may comprise electrothermal or electrostatic actuators for generating movement of the arms for grasping a microcomponent. Thus, rather than having the actuation mechanism in an external, macro-scale device as in the gripper disclosed in the Conway et al. patent, microgripper devices have been proposed in the existing art that include, in a micro-scale device, arms and an actuation mechanism for moving the arms (although, the power supply and/or control circuitry for powering the actuation mechanism to generate movement of the arms may be arranged external to the microgripper).
An example of one type of microgripper in the existing art is a microtweezer taught by Keller, et al., in “Microfabricated High Aspect Ratio Silicon Flexures,” MEMS Precision Instruments, 1998; and “Hexsil Tweezers for Teleoperated Microassembly,” by C. G. Keller and R. T. Howe, IEEE Micro Electro Mechanical Systems Workshop, 1997, pp. 72-77. The microtweezers proposed in Hexsil Tweezers for Teleoperated Microassembly has two parallel arms that are operable, through electrothermal actuation, to move toward or away from each other, which may enable the arms to grasp a microcomponent between them. More specifically, each arm is positionally fixed at one end and is movable at the opposing end (which may be referred to as the arm's “released end”). Each arm effectively comprises an electrothermal actuator (or thermal expansion actuator beam) that is operable, responsive to electric power being applied thereto, to cause the released end of the arm to move in a direction away from the opposing arm. Therefore, electric power may be applied to the microtweezer device to cause the released ends of the tweezer arms to spread apart.
In the above-described microtweezer device, applying greater power to the electrothermal actuators causes the arms to spread further apart, while reducing the amount of applied power causes the arms to return toward each other. Accordingly, to maintain a given position of the arms (other than their powered-off position) or to maintain a particular gripping force against an object being grasped (other than the force applied when the device is powered-off), power must be maintained to the arms.
U.S. Pat. No. 5,072,288 issued to MacDonald et al. provides another example of a microgripper proposed in the existing art. The microgripper disclosed in the MacDonald et al. patent has two parallel arms that are operable, through electrostatic actuation, to move toward or away from each other, which may enable the arms to grasp a microcomponent between them. Each arm is positionally fixed at one end and is movable at an opposing end (referred to as the arm's “released end”). Each arm comprises an electrically-conductive beam (e.g., having metal lines) that is operable, responsive to electric power being applied thereto, to cause the released end of the arm to move in a direction away from the opposing arm or in a direction toward the opposing arm. Therefore, electric power may be applied to the microgripper device to cause the released ends of its arms to spread apart or to compress together to achieve a tweezing action.
The microgripper device disclosed in the MacDonald et al. patent uses electrostatic forces between the arms to generate the tweezing action. Application of a step function potential difference between the arms (by applying potentials to the electrically-conductive beam forming each arm) may generate either an attracting or repelling electrostatic force between the charged arms, depending on the polarity of the potential. Accordingly, to maintain a given position of the arms (other than their powered-off position) or to maintain a particular gripping force against an object being grasped (other than the force applied when the device is powered-off), power must be maintained to the arms.
With microgrippers of the existing art, such as those proposed in Hexsil Tweezers for Teleoperated Microassembly and in the MacDonald et al. patent, the range of motion of the microgripper arms is relative to their length. That is, the longer the arms, the greater the range of motion that may be achieved through the above-described electrothermal or electrostatic actuation of the arms. For instance, the microtweezers proposed in Hexsil Tweezers for Teleoperated Microassembly have arms that are 8 millimeters (mm) in length by 1.5 mm wide by 45 micrometers (μm) thick. The released ends of the arms are able to be displaced through electrothermal actuation to allow for a separation distance of 35 μm. To achieve greater separation, the arms may be implemented having a greater length. In general, the range of motion associated with an electrothermal actuator is limited to approximately 0.5 to approximately 10 percent of the overall length of the actuator's arms. However, in general, increasing the length of the arms decreases their rigidity (particularly if their thickness is not also increased), which may in turn decrease their gripping force.
Microgrippers requiring power may experience dynamic fluctuations in the conductivity of the device. Additionally, these devices may produce stray electrostatic fields that can influence the object one is trying to manipulate.
It would be desirable to have gripping devices, methods of manufacture, and gripping processes that improve upon the above-described devices and processing techniques and that does not require the use of electrical power for operation.